A MODEL OF THE CATHODE REGION OF ATMOSPHERIC-PRESSURE ARCS

The paper deals with calculation of parameters in the near-cathode pla sma layer, on the cathode surface and in the body of a cathode in high -pressure are discharges. These parameters can be calculated independe ntly of the are column if the heat flux coming from the column to the edge of the near-cathode layer does not play a decisive role in the en ergy balance of the layer, which, according to the estimates presented , is a likely case. The physics of the near-cathode layer is reconside red in view of major contradictions that have appeared in the literatu re recently, in particular with regard to the role of the near-cathode space charge sheath. A model of a near-cathode layer is developed tha t is based on a multifluid description of the plasma and takes into ac count multiply charged ions. The model is employed to calculate parame ters of the layer as functions of the voltage drop in the layer and of the local value of the surface temperature. By means of these data, a n approximate asymptotic theory of are spots is extended to cathode sp ots in high-pressure plasmas. Calculated spot parameters are presented for the following combinations cathode/plasma: tungsten/argon, thoria ted-tungsten/argon, thoriated-tungsten/nitrogen, and zirconium/nitroge n. The obtained results agree with the recent measurements of the spot temperature.